1. Field of the Invention
The present invention relates to a process for manufacturing multilayer pellets and a die equipment for manufacturing multilayer pellets. In more detail, the present invention relates to a process for manufacturing multilayer pellets served as a molding material for various plastic products and having a core-sheath structure comprising a plurality of molding materials and a die equipment used for manufacturing multilayer pellets with the extrusion molding technique.
The present invention also relates to masterbatch resin pellets with improved brittleness and a process for manufacturing thereof using a multilayer pellet.
The present invention further relates to a process for drying and manufacturing thermoplastic polyester resin with good drying acceleration using a multilayer pellet.
2. Description of the Related Art
Pellets for plastic molding are obtained by heating and melting plastic materials previously blended and extrusion-molding the melted materials into strand forms, and then cutting the obtained plastic strands into small tablet forms, so-called pellets.
When various plastic products are molded, preparing the pellets as described above has many advantages. For example, blending and adjusting materials are not required every time when plastic products are molded; stable operation of plastic molding can be performed; stabilized product quality can be obtained; and raw materials can be easily supplied to the molding machine and other handling becomes easier.
Plastic pellets entirely molded from one plastic material are common. However, double-layer pellets or multilayer pellets comprising a plurality of plastic materials and a process for manufacturing such pellets have also been proposed.
JP-A-7-171828 (“JP-A-” indicates Japanese Unexamined Patent Publication) discloses multilayer pellets of a core-sheath structure in which a material with rich adhesiveness is used as the core and a crystalline polyolefin resin with less adhesiveness is used as the sheath in order to solve the problem of likeliness to cause blocking of pellets manufactured from materials with rich adhesiveness.
JP-A-59-81121 discloses a process for manufacturing pellets from an olefin-vinyl alcohol copolymer which is unable to form strands for manufacturing pellets due to its too small melt tension. In the process, multilayer pellets of a core-sheath structure is manufactured by cutting multilayer strands having a core with resin having small melt tension, i.e. the olefin-vinyl alcohol copolymer, outer circumference of which is covered with resin having large melt tension. JP-A-59-81121 also shows a manufacturing equipment having a dice-head for pellet molding equipped with a structure for feeding sheath material to the circumference of core material.